Field of the Invention
The present invention relates to a coil component and a manufacturing method of the coil component, and particularly to a coil component that uses a drum core and a manufacturing method thereof.
Description of Related Art
In recent years, electronic components that are used in information terminal devices such as smartphones have been strongly required to be smaller in size and lower in height. Therefore, as for coil components such as pulse transformers, surface-mount coil components that use drum cores instead of toroidal cores have been frequently used. For example, Japanese Patent Application Laid-Open No. 2012-119568 discloses a step-up transformer of a surface-mount type that uses a drum core.
The coil components that use drum cores have been required to be even smaller in size and lower in height. The size of a winding core portion has been decreasing from year to year. In order to secure a required inductance, a coated conductive wire that is thinner in diameter needs to be used.
However, the coated conductive wire that is thin in diameter is low in dielectric strength voltage. Accordingly, coil components that need to insulate primary and secondary windings, such as pulse transformers, may be insufficient in dielectric strength voltage. In particular, if wires are connected to terminal electrodes by thermo-compression bonding or laser bonding, heat that is applied at the time of wire connection is conveyed via core material of the coated conductive wire, and the coating film would be degraded. Therefore, the problem is that the component is likely to be insufficient in dielectric strength voltage.
The inventors hereof have studied the use of conductive wires coated with resin having a low melting point in order to provide a coil component having a high dielectric breakdown voltage. This is because scars and cracks, if any, in the resin coating, can be filled with the resin when the coated conductive wire is heated. This prevents a decrease in the dielectric breakdown voltage of the coated conductive wire.
Our study reveals, however, that if the resin film is too thick, it applies a high stress on the conductive wire as it is cooled. Consequently, the conductor filaments are greatly displaced.
The moving of coated conductive wires used does not influence the basic property (e.g., inductance) of the coil component. However, the study of the inventors hereof shows that if the coated conductive wires move much, the dielectric breakdown voltage of the coated conductive wire will more decreases a little than otherwise. This is probably because the distance between any adjacent coated conductive wires becomes short at some positions as the coated conductive wires move, intensifying the electric field between the primary winding and the secondary winding.